Centralized traffic controlling system for railroads



April 25, 1939. N. D. PRESTON ET AL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 2 Sheets-Shet 1 Filed Nov. 30, 19-32 Q: EN 1% in in u m INVENTORS N.D. Preston and CliBush neH BY W Tfiggi w w Ruse.. xuGm mm. m

Patented Apr. 25, 1939 UNITED STATES PATENT OFFICE CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Application November 30, 1932, Serial No. 645,037

31 Claims.

This invention relates to centralized traflic controlling systems for railroads, and more particularly to the communication part of such systems.

In such a system, railroad traffic is controlled 5 from a central control ofiice, and also the location of trains, as well as the condition of trafiic controlling devices at remote locations, are indicated to the attendant at the control ofiice. Such a system is supplemented by the well-known au- 10 tomatic block signal system and other local means, which are ordinarily provided to guard against unsafe trainmovements, improper operation of track switches or the like.

The switches and signals are distributed throughout the territory, but those located relatively near or adjacent each other, as well as the apparatus provided to govern these switches and signals, are conveniently referred to as comprising a field station. A communication system is provided to interconnect the control ofiice with the several field stations, and is so organized that complete supervision is obtained by the operator, of the various signal and switch devices at the remote stations. 5 In accordance with the present invention, the

communication system includes two line wires extending from the control oflice through the several field stations in series, which two line conductors are connected together at the last field station of the series in order to provide a normally closed line circuit. These two line conductors form a single circuit, used to select a desired one of the field stations, after which a relay or control device for each switch or signal at the selected station, may be actuated or conditioned for controlling their respective devices, thereby governing the traflic at the selected station. Such selection and control is referred to as transmission of controls.

The communication system is also used to transmit to the control office, indications of the positions of the switches and signals and for indicating the presence or absence of trains in particular track sections, as well as any other indications which may be useful in directing and supervising train movements, which indications are of course preceded by the registration in the control office of that particular field station that is transmitting. This function is automatically effected, when a new indication is ready to be transmitted to the control oifice and is conveniently referred to as transmission of indications.

The system is of the coded duplex type and is operated through cycles, during each of which, transmission of controls and transmission of indications can occur separately or simultaneously. This feature is so incorporated in the system that duplex or two-way transmission can simultaneously occur to and from the same station, or to and from different stations.

When controls are transmitted, a station selecting code is first applied to the line for selecting the particular station desired, after which the controls are transmitted to the selected station by means of code impulses. When indications are transmitted, the field station transmitting such indications first sends a station registering code for registering that station in the ofiice. Thereafter, the particular indications are transmitted to the control ofiice, by means of an additional code and are displayed on indicator devices, such as lamps or the like, associated with the station sending.

For the transmission of controls, a predetermined number of impulses of selected polarities are placed on the line circuit for operating the apparatus at the control ofiice and at the field stations, through a cycle of operations, irrespective of the character of the impulses, while the distinctive character of such impulses of a series included in the cycle determines the particular station to be selected and the controls to be transmi ted to the selected station.

For the transmission of indications, the durations or lengths of time effected during the on and on impulse periods of a cycle are used to form a characteristic code combination which determines the particular station to be registered in the control oflice and the indications to be transmitted after such registration. The on periods refer to the periods when the line circuit is energized; while the o periods refer to the periods when the line circuit is de-energized.

I One feature of the present invention relates to the manner in which both the time intervals between energized line periods and the time intervals of the energized line periods are varied in length, so as to double the indication transmismission capacity over that ordinarily obtained.

For example, in systems of this type, one energization or on period and one de-energization or off period of the line circuit has usually been designated as comprising a single step, with the field stations s0 arranged that indications are 50 transmitted by distinctively changing or varying the condition of the line circuit once for each step.

In the present embodiment, the condition of the line circuit is distinctively changed or varied twice during each step, once during the energized or u "on period and once during the de-energized or off period.

A system arranged in this manner increases the capacity for the transmission of indications to substantially double the control transmission capacity of the system. This is particularly desirable in a centralized traffic controlling system, since it has been found in practice that the number of indications desired by the operator for proper information is substantially double the number of controls necessary for positioning the trafiic governing devices under his supervision.

Another feature of the present invention relates to the manner in which controls are transmitted in coordination with the stepping relay operation without storing the polarity of the control impulses either in the control office or at the field station. This is accomplished in the control oifice by arranging the stepping relays and their contacts in such a way, that stepping is offected on the on periods and the half step relay is shifted on the off periods. In this connection the relays which select the polarity to be applied to the line circuit are maintained energized through contacts of a stepping relay which does not shift on the next energization of the line. A similar arrangement is used at the field station so that controls are registered on the on periods, through contacts of a stepping relay which does not shift on this on period.

Since the present invention is directed to the transmission of controls and double indications by means of a single circuit extending from the control office to the field stations, obvious economies in the construction and maintenance of the line are realized.

Other objects and advantages of the present invention will be hereinafter set forth in the specification and claims and shown in the drawings. The characteristic features will be explained more in detail in the following description of one embodiment of the invention, while various other characteristic features and advantages of the system comprising this invention, will be in part pointed out and in part apparent as the description progresses. I

In describing the invention in detail, reference will be made to the accompanying drawings which illustrate, in a diagrammatic manner, the apparatus and circuits employed. Those parts having similar features and functions are designated in the different figures by like letter reference characters, generally made distinctive either by the use of distinctive exponents representative of their location or by the use of suitable preceding numerals representative of the order of their operation, and in which:

Fig. 1 illustrates the apparatus and circuits employed at the control office;

Fig. 2 illustrates the apparatus and circuits employed at one of the field stations.

GENERAL DESCRIPTION.

The single line circuit connecting the control oilice with the field stations is shown in the upper portion of Figs. 1 and 2 and the operation of the system may be conveniently followed by placing the drawing of Fig. 2 to the right of Fig. 1. Within the dotted rectangle, in the central upper portion of Fig. 2, the extension of the single line circuit through other stations is indi cated. It will be understood that the line circuit extends through one or more stations, in addition to the one illustrated in Fig. 2 and that these additional stations have apparatus andcircuit arrangements practically the same as that shown in Fig. 2. As will be more specifically pointed out in the following description, the points of difference in the circuit connections at different field stations are the distinctive connections of the code jumpers and the contacts of the station relays ST (with suitable exponents and preceding numerals), so that a particular field station will be fully responsive only to the particular code assigned to that station.

For the purpose of simplifying the illustration and facilitating the explanation, various parts and circuits have been diagrammatically shown and certain conventional illustrations have been employed. The drawings have been made more with the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, the use of symbols being employed to indicated the connections to the terminals of batteries or other sources of current instead of showing all of the wire connections to these terminals.

The symbols and indicate the positive and negative terminals, respectively, of suitable batteries or other sources of current; and the circuits with which these symbols are used always have current flowing in the same diection. The symbols (3+) and (B-) are employed to indicate the positive and negative terminals, respectively, of a suitable battery or other source of current having an intermediate tap (CN) and the circuits with which these symbols are used may have current flowing in one direction or the other, depending upon whether the terminal (13+) or (B) is used in combination with the intermediate tap (CN) No attempt has been made to show all of the apparatus employed, such as the total number of manual controls at the control office, the total amount of the equipment or its exact arrangement at the field stations, since these may vary to suit local conditions. The character of that apparatus illustrated in the typical control office and field station will now be considered.

Control ofiicc equipment-As typical of the equipment located in the control office illustrated in Fig. 1, a control machine, having a group of control levers for each field station, is provided. A miniature track switch indicated by reference character ts, corresponds to a particular track switch in the field, and is considered to be representative of the actual track layout in the field. Various indicating lamps, such as I, or equivalent devices, together with apparatus and circuits to accomplish the desired operation of the system, are likewise provided. The portion of the control office apparatus illustrated in Fig. 1, shows more particularly that part of the control machine which is typical of the apparatus associated with a single field station having a track switch, a cross-over or the like, together with the common transmitting apparatus employed for controlling the circuit operation for all such stations.

This equipment for one track switch comprises a switch machine lever SlVIL, a self-restoring starting button SB, the miniature track switch ts and the indication lamp 1. Similarly, one or more signal control levers (not shown) would also be associated with the single field station apparatus, but in order to simplify the drawings and description, these devices have been omitted. It is obvious that the control of a track switch, by means of a lever 'SML, may be considered as typical of the control of other traffic controlling devices.

The movement of the lever SML to one extreme position or the other, followed by the actuation of the starting button SB, results in the normal or reverse operation of the track switch, corresponding to lever SML at that field station which is associated with starting button SB, and this operation is controlled through the medium of the communication system of the present invention. The momentary actuation of the starting button SB is preferably stored by a storing relay (not shown) which, in turn, picks up the corresponding code determining relay CD of the associated station. Such control has been merely indicated in order to simplify the present disclosure.

The storing relays for each starting button and their corresponding code determining relays CD are so interconnected, that, irrespective of the number of storing relays energized simultaneously or in rapid succession, only one relay CD for one particular station may be picked up during one cycle of operations. This interlocking circuit connection is so arranged that if several storing relays are up at the same time, their corresponding relays CD will be picked up one at a time, during successive operating cycles, in an order predetermined by their relative locations in the bank of relays, all of which has been completely disclosed in the prior application of N. D. Preston et al., Ser. No. 455,304, filed May 24, 1930, Patent No. 2,129,183 dated September 6, 1938.

The control oflice includes a line relay F and a line repeating relay FP, both of which are normally picked up or energized during the normal period of rest of the system and also during the period of blank between successive operating cycles.

Slow acting line repeating relays SA and SAP are picked up at the beginning of each cycle and dropped at the end of each cycle. These two relays have such slow-acting characteristics that the pick-up time of each is relatively long compared to the pick-up time of the neutral relays F and FF, for example, but the pick-up time of these slow relays is relatively short in comparison with the time required for their release. The releasing or drop-away time of the relay SA is sufficiently long, so that its contacts remain .in their picked up positions between successive impulses or during all oif periods of a cycle, except the last period, which is a comparatively long ofi period, for the purpose of returning the system to the normal period of rest, or period of blank.

Associated with the line relay F and its repeating relays is a bank of stepping relays, including stepping relays IV, 2V, 3V and LV, together with a half step repeating relay VP, which are provided to mark off the successive steps of each cycle. An impulsing relay E is jointly controlled by the stepping relays and the half step relay, for cooperating with impulse repeating relay EP and pulsing relay PL to govern the opening and closing of the line circuit.

The polarity of the impulses applied to the line circuit from a battery B is determined by positive code sending relay PC and negative code sending relay NC. These two relays are controlled on the steps of an operating cycle in accordance with the station code and the controls to be transmitted for that particular cycle.

Relay EP, in addition to controlling the line pulsing relay PL, selects the polarity of the potential to be applied to the pilot relays as determined by the short and long on periods. Relay EPT selects the potential to be applied to the pilot relays as determined by the short and long off periods. A starting relay STR is picked up to initiate a cycle of operations, both when controls are to be transmitted due to the manual initiation of the cycle in the control oflice, and when indications are to be transmitted due to the automatic initiation of the cycle by a field station.

For the purpose of illustrating station registration and as typical of the pilot relay arrangement, pilot relays lPF and IPB are connected to the indication buses, so that they may or may not be picked up on the first step. Reference character IPF indicates a first pilot relay, picked up through the front contact of line relay F during an on period. Reference character IPB indicates a first pilot relay, picked up through the back contact of line relay F during an off period. Similarly, pilot relays ZPF and ZPB are picked up, or not, as determined by the indication code for the second step. Similarly, additional pilot relays (not shown) may be provided for additional steps up to the point where a sufficient number of codes for station registration have been provided. These pilot relays are of the two position polarized magnetic stick type, although it should be understood that any suitable type or arrangement may be provided for accomplishing the results obtained by this typical arrangement.

The indication receiving relays, such as for example relay lR-F, are also of the two position polarized magnetic stick type and are for storing the indications transmitted from the field stations. The particular indication receiving relay shown in Fig.1 is merely typical of the circuit arrangement of all such relays. The reference character IRE associated with this one relay, refers to its being operated through the front contact of relay E. Another indication receiving relay would have the reference character iRB, meaning that this relay operates on the first step following station selection and that it is operated through the back contact of relay E.

The control ofiice also includes various sources of current supply, bus wires, circuit connections, indicator lamps, terminal boards, overload protection and various other devices and apparatus which are necessary in railway signalling practice, but which have not been indicated in this disclosure.

Field station apparatus. since the apparatus and devices located at the field stations may vary according to local conditions, that illustrated in Fig. 2 is merely typical of all the field stations of the system. It will be understood that the arrangement of circuits and apparatus illustrated in Fig. 2 may be used at the first, or any other field station by merely arranging certain code jumpers and selective circuits for the desired code, but for convenience of description, the station illustrated in Fig. 2 is assumed to be the first field station and for this reason, the distinctive exponent has been employed in connection with the relays and other devices shown. A turn-out track is illustrated as connected to a main track by means of a track switch TS which is operated from one extreme locked position tothe other by a suitable switch machine SM The switch machine is controlled by a switch machine control relay SMR which is of the two position polar magnetic stick type, and which is positioned from the control o ifice by means of the communication system disclosed herewith. The relay SlVlR controls the operation of the switch machine by energizing its normal or reverse operating circuits from a local source of current in the field station in any suitable manner. This control preferably includes suitable approach locking means and other automatic signalling means, usually employed but not shown in order to simplify the present disclosure as much as possible. The switch machine SM while indicated as being controlled only from the control office, may employ a dual control selector in the well-known manner without in any way adding to, or detracting from, the present invention.

Suitable signals are associated with the track switch T8 for governing traffic over this section of track and these signals are provided with automatic signalling means, so that the traific over this track switch may be coordinated with other sections of the track and other trafiic controlling devices. These signals are capable of being controlled from the control ofiice through the medium of the communication system of the present disclosure, by means of control relays operated from the control ofiice in. a manner similar to relay SMR but the complete circuit arrangement and description of this operation is omitted for the sake of simplicity. A detector track section, having a. normally energized track circuit with the usual track relay T and track battery, is also associated with the track switch TS for-indicating the passage of trains over this section of track.

The communication part of the system at the field station includes a three-position biased-toneutral polarized line relay F together with its quick acting line repeating relay FP Relay F is normally positioned to the right by reason of the normally energized line circuit during the normal period. Relay FP at the field station is normally de-energized. Slow acting relays SA and SAP, having characteristics similar to corresponding relays in the control oilice, are provided to define the bounds of each cycle of operation. Relay SA is suificiently slow in releasing when de-energized, so that it holds its armature attracted during all ofi periods (irrespective of their lengths) except the last, or change to normal period. The field station, likewise includes abank of stepping relays lV 2V 3V and LV together with the half step relay VP operating in a similar manner and in synchronism with the stepping relay bank in the control office.

For the purpose of illustrating the selection of a station, three station selecting relays IST 2ST and 381, of the two-position polar magnetic stick type have been illustrated and it is to be understood that this arrangement for stat tion selection is merely typical and that other suitable means may be employed.

A change relay CH is provided to register a change in the traffic controlling devices at the station, so that the system will be initiated for the transmission of new indications, as required. Although this change relay is shown as being responsive only to a change in the position of track relay T it is to be understood that its holding stick circuit may be carried through any number of relays or other devices, so that it will register a change in one or more of a large number of devices.

A change repeating relay CHP together with a lockout relay L0 are employed at each field station in connection with the indication circuit circuit to register the station in the control ofiice and to transmit the required indications.

A resistance R is used for the purpose of compensating for the distance between the field stations and the control office. The last station, or the one at the end of the line, has no such resistance but the line wires are connected together as indicated within the dotted rectangle in the upper portion of Fig. 2. Other stations are provided with these resistance coils, the resistances of which are increased by a suitable amount to compensate for the line resistance, in such a way that the first station has a resistance coil R with a maximum resistance, while the others are gradually decreased in resistance as they are located farther from the ofiice. Relay lPLT is for the purpose of extending an otherwise normally short oii period into a comparatively long off period.

The field station also includes suitable bus Wires, circuit connections, code jumpers and other devices which are necessary in railway signalling practice but which have not been indicated in this disclosure. for the sake of simplicity.

It is believed that the nature of this invention, its advantages and characteristics, may be best understood with further description being set forth in the manner of operation.

GENERAL OPERATION field stations at substantially the same time, they are transmitted to the different field stations on separate cycles of operations, one station for each cycle. Likewise, if several field stations have indications to be transmitted at substantially the same time, they are transmitted to the control office, one station at a time on separate operating cycles. g

It may happen that there are new controls and new indications ready for transmission at a given time and in this event controls are transmitted simultaneously with indications. On such occasions, indications may be transmitted from the same field station to which controls are transmitted, or they may be transmitted from some other field station during the same cycle of operations.

Irrespective of whether the cycle is for transmission of controls and/or the transmission of indications, a predetermined number of impulses is applied to the line circuit, to accomplish the synchronous operation of the stepping relays at the control office and at the field stations. These impulses are time spaced, the intervals between impulses being of variable durations and the periods during which the line is energized being also of variable durations.

When a cycle of operation is initiated for the transmission of controls, the character of the impulses applied to the line is determined by the particular station to be selected and the particular controls to be transmitted to the selected station, in accordance with the code jumper connections and the positions of the control levers respectively for that station.

When a cycle of operation is initiated for the transmission of indications alone, the character of the impulses applied to the line circuit is the same for all impulses and this particular combination does not effect the selection of any field station, but merely functions to cause the stepping relays in the control office and at the field stations to be operated in synchronism. When such a cycle of operations is initiated from a field station for the transmission of indications, the line circuit is energized and de-energized with a series of impulses of a single character. Since this results in a combination of a distinctive character being applied to the line circuit, when no station is to be selected for transmission of controls, this particular code is not effective to select a station and it is conveniently referred to as a phantom code.

If, while transmission of controls is taking place, no indications are being transmitted, the de-energized, or off, periods of the line circuit are all of comparatively short duration and the energized, or on, periods of the line circuit are of comparatively long duration. Indications are transmitted from the field stations to the office over the single line circuit, by predetermining whether the off periods will be short (normal) or long (abnormal) and predetermining whether the on periods will be long (normal) or short (abnormal). The combinations of these short and long off and on periods are effective to determine the station to be registered in the control office and thereafter display the indications from the registered station.

The line relay in the control ofiice is normally operated and those at the field stations are normally positioned to the right, by means of current flowing over the line circuit, from battery B in the control office, through the normally energized, positive control relay PC.

When controls or indications are to be transmitted, the line circuit is momentarily opened and the battery connection reversed, after which the line circuit is energized by current from the battery flowing in a reverse direction from normal, which is effective to pick up the line relays at the field stations and position them to the left. This first energized period is conveniently referred to as the initiating period, during which certain relays are conditioned, as will be later described in detail.

The momentary interruption of the line and the reversal of the battery connection to the line circuit is also conveniently referred to as the lockout period, since it is during this period that one station is effectively connected to the communication system for the transmission of indications, to the exclusion of all other stations.

After the initiating period, the system continues through a complete cycle of operations, consisting of a number of off and on periods,

this number being determined by the number of steps required and this number of steps, in turn, being governed by the size of the system. After the last on period, a comparatively long off, or de-energized period, is effective to condition the relays for changing to normal, or the period of blank. After this off period, the line is energized by current from battery'B, in What may be conveniently termed a direction, since the positive control relay is picked up and the line relays F F etc., at the stations are positioned to the right. This is the normal period or period of blank.

In the system of the present invention, the stepping relays IV, 2V, etc., in the control oflice and HF, 2V etc., at each field station operate in synchronism throughout a cycle, being picked up during the on periods and dropped at the end of the cycle. The half step relays VP in the control office and at the field stations are likewise operated in synchronism throughout a cycle, being shifted during the off periods, that is, they pick up at the start of the odd off periods and drop at the start of the even off periods. The on periods are those periods during the cycle, when the communication line is energized and the off periods are those periods during the cycle, when the communication line is de-energized.

For convenience in describing the operation of the present invention, an operating cycle is divided into periods as shown in the following table:

1. Normal or period of blank.

2. Initiating and lockout period.

Manual start from control ofiice. Automatic start from field station. On shifting to Associates sending station with control line circuit and locks out all other stations.

3. Conditioning period.

Conditions lockout, line and line repeating relays. Long on 4. First off period.

Relays VP and VP picked up. Control No. 1 conditioned. Off indication No. 1 conditioned.

5. First on period.

Relays IV and lv 'picked up. Control No. 1 executed.

Off indication No. l executed. On indication No. 1 conditioned.

6. Second off period.

Relays VP and VP dropped. Control No. 2 conditioned.

On indication No. 1 executed. Off indication No. 2 conditioned.

7. Second on period.

Relays 2V and 2V picked up. Control No. 2 executed.

Off indication No. 2 executed. On indication No. 2 conditioned.

8. Third off period.

Relays VP and VP picked up. Control No. 3 conditioned.

On indication No. 2 executed. Off indication No. 3 conditioned.

9. Third on period.

Relays 3V and 3V picked up. Control No. 3 executed.

01f indication No. 3 executed. On indication N0. 3 conditioned.

10. Fourth off period.

Relays VP and VP dropped. Control No. 4 conditioned.

On indication No. 3 executed. Off indication No. 4 conditioned. Fourth on period.

Relays LV and LV picked up. Control No. 4 executed.

Off indication No. 4 executed. On indication No. 4 conditioned. Change to normal period (off); On indication No. 4 executed. Restores various relays to normal. Long off. Followed by period of blank.

DETAILED OPERATION Normal period of rest.With the communication part of the centralized traffic controlling system, with which this invention is concerned, at rest, all of the relays in the control oflice and at the field station are in their normal or de-energized positions except relays F, F FP, PC, EP, CH CI-IP and T Relay F is held up and relay F is positioned to the right by current in the circuit extending from the positive terminal of battery B, front contact 26 of relay PC, back contact Z'l of relay NC, winding of relay F, back contact 28 of relay PL, line conductor 1, winding of relay F back contact MS of relay PL through other field stations and including their relays such as F and back contacts of relays such as PL conductor 8 closed at the last station, line conductor 5, back contact 2Q of relay NC, front contact 39 of relay PC and negative side of battery B.

Relay FF is energized over a circuit extending from front contact E8 of relay F and winding of relay FP to Relay PC is energized over a circuit extending from back contact l3 of relay VP, back contact M of relay 3V, back contact l5 of relay lV, back contact ll of relay STR, bus and winding of relay PC to Relay EP is energized over a circuit extending from back contact 3'3 of relay E and Winding of relay EP to Relay CH is energized over a circuit extending from front contact i253 of relay T conductor I52, front contact I91 of relay CH and lower winding of relay CH to Relay CHP is energized over a circuit extending from back contact H56 of relay PLT front contact MS of relay CHP and upper winding of relay CHP to Track relay T is normally energized by means of a circuit (not shown) connected to the normally energized track section.

Manual starting-It will be assumed that the system is in its normal condition and that the operator desires to transmit controls to a particular field station. Control lever SML, indicated in Fig. l, is typical of other control levers provided. When the starting button SB, associated with the desired station, is actuated, a suitable storing relay is positioned and the CD relay, associated with the desired station, is immediately picked up. However, such CD relays for several stations are so interconnected, that if several starting buttons are simultaneously operated or operated in quick succession, only one CD relay is picked up at any one time. Thus, these CD relays are picked up successively for successive cycles of operations. The interconnecting circuits for accomplishing this selective operation are not disclosed in this embodiment, but may be of the arrangement fully shown and described in the prior application Ser. No. 455,304, above mentioned.

In considering the operation of the present invention, it will be understood that the actuation of starting button SB, shown in Fig. 1, causes the actuation of the correspnding CD relay, only one of which can be up at any one time. ation of the starting button SB, in picking up its corresponding CD relay, also picks up starting relay STR and this relay is elfective to initiate the cycle of operations. The circuit for picking up relay STR' extends from back contact 10 of relay SA, front contact H of relay CD, front contact it. of relay PP and winding of relay STR, to Relay STR completes a stick circuit for itself extending from back contact l3 of relay VP, back contact Id of relay 3V, back contact i5 of relay IV, front contact N5 of relay STR and winding of this relay, to

is stick circuit for relay STR, including back contact l3 of relay VP, is opened during the first off period when relay VP is picked up, which results in the release of relay STR. Relay STR can not again be picked up during this same cycle, since its energizing circuit will be open at back contact ll! of relay SA, which is held up until the end of the cycle.

The picking up of relay STR opens the normally energized circuit of relay PC at back contact ll of relay STR. Front contact ll of relay STR switches the above described circuit, extending from through back contact l3 of relay VP, to the winding of relay NC and this relay is immediately picked up.

During the interval between the dropping of relay PC and the picking up of relay NC, the line circuit is deenergized, which may allow relays F in the control oiiice and F at the field station to be dropped, butthis interval is of such short duration that the circuits which these relays close are not effective to pick up other relays, such as PLT at the field station. The release of relay PC and the actuation of relay NC results in reversing the connection of battery B to the line circuit, which operates the line relays at the stations, (such as F indicated in Fig. 2) to the left.

This brings the cycle of operations into the conditioning period and results in picking up relays F, FP, SA and SAP at the control ofiice and relays l F1 SA and SAP at the field station. The circuit for energizing relay FP in the control office is from front contact l8 of relay F and winding of relay FP, to Before relay SA is picked up, relay FP is held up through back contact 2! of relay SA and front contact 25 of relay PP. The circuit for picking up the SA relay extends from front contact IQ of relay NC, front contact Ell of relay PP and winding of relay SA, to The circuit for picking up the SAP relay extends from front contact 2| of relay SA and winding of relay SAP, to

The circuit for picking up relay FP at the field station extends from contact I22 of relay F now in its left hand dotted position, and winding of relay FP to The circuit for picking up relay SA extends from front contact I23 of relay F19 and winding of relay SA to The circuit for picking up relay SAP extends from front contact I24 of relay SA and winding of relay SAP to Polarity selection of impulscs.When the system is initiated into a cycle of operations from the control office, resulting in the operation of starting relay STR, the first impulse placed upon the control line is as indicated in the initiating period of the above table. This is because relay PC is dropped and relay NC is picked up The actueach time the control ofiice initiates a cycle of operations.

During the initiating period, when relay PC is released and relay NC is picked up, the battery connection to the line is reversed, which results in holding relay F in the control oflice and actuating relays F F etc., at the field stations to their left hand positions. This application of current from battery B to the line circuit causes the system to go through various relay operations, but the description of these operations will be omitted at present, it being assumed that thecontrol line circuit is impulsed by means of back contact 28 of relay PL, and that this impulsing circuit results in the stepping relay operation.

During the conditioning period, the operation of relay SAP closes a circuit for picking up relay E, extending from front contact 3| of relay SAP, back contacts 32, 33, 34 and 35 of the four stepping relays in series, back contact 36 of the half step relay VP and winding of relay E, to The operation of relay E closes a circuit for picking up relay EPT extending from front contact 3'! of relay E and winding of relay EPT, to Relay EPT completes a stick circuit for itself as long as relay F is operated, extending from front contact 38 of relay F, front contact 39 of relay EPT, and winding of relay EPT, to

It will be recalled that the line is energized during this, the conditioning period, and by referring to the above table it will be noted that this period is a long on. This is for the reason that the line will remain closed until slow acting relay EP is dropped, after its circuit is interrupted at back contact 31 of relay E, which is now actuated. When relay EP releases its armature, a circuit is closed for actuating relay PL extending from back contact 40 of relay EP and winding of relay PL, to The actuation of relay PL and the resulting deenergization of the line advances the system into the first off period.

When the line is deenergized, by relay PL opening its back contact 28, relay' F is released and since the stick circuit of relay FP, through its own front contact 25, is now interrupted at back contact 2! of relay SA, the opening of front contact I 8 of relay F results in the release of relay FP. A circuit is now closed for picking up the half step relay VP, extending from front contact 3| of relay SAP, back contact 4| of relay FP, back contact 42 of relay IV and winding of relay VP, to Relay VP closes a stick circuit for itself, which is effective as long as relay IV is down and which extends through its front contact 43 and the remainder of the circuit just described.

With the code jumper 44 connected as shown, control No. 1 is conditioned by the actuation of relay PC and the release of relay NC. Relay NC is dropped when its circuit is interrupted, at back contact !3 of relay VP and relay PC is picked up over a circuit extending from front contact l3 of relay VP, back contact 45 of relay 2V, No. 1 control bus 46, front contact 4! of relay CD, code jumper 44 and winding of relay PC, to The release of relay NC and the actuation of relay PC, results in the preseleotion of a impulse for the next, or first on period, and the connection of the line circuit to battery B, through front contacts of relay PC' and back contacts of relay NC, is in such a direction that relay F of Fig. 2 will be actuated to its right hand position.

The control of the NC and PC relays is effected during other off periods, by means of other code jumpers, such as 48 and 49. Thus, in the second off period, relay VP will be dropped and since relay lV will be up, (picked up during the first on period), a circuit is effective for picking up relay NC, extending from back contact l3 of relay VP, back contact I4 of relay 3V, front contact of relay IV, No. 2 control bus 50, front contact 5! of relay CD, jumper 48 and winding of relay NC, to The actuation of relay NC and the release of relay PC, (since the circuit of relay PC is incomplete during this period) results in preselecting a code for the second on period.

During the third off period relay VP will 5.

again be picked up and relay 2V will be up, (being picked up during the second on period), which closes a circuit for conditioning the No. 3 control, extending from front contact I3 of relay VP, front contact 45 of relay 2V, No. 3 control bus 52, front contact 53 of relay CD, code jumper 49 and winding of relay PC, to Since this results in the actuation of relay PC and the release of relay NC, a code impulse is preselected for the third on period.

During the third on period, relay 3V is picked up and during the fourth off period relay VP is dropped. Control No. 4 is conditioned during the fourth of? period by means of a circuit extending from back contact l3 of relay VP, front contact id. of relay 3V, No. 4 control bus 54, front contact 55 of relay CD, and contact of switch machine lever SML, to either the bus or the bus, as determined by the position of lever SML. If this lever is connected with the bus, as indicated in Fig. 1, the code impulse of the fourth on period will be because relay PC will be picked up and relay NC will remain normal.

It will be apparent that the code jumpers 44, 48 and 49, connected as shown in Fig. 1, result in the selection of a station having a code combination It will be obvious that, while only one step is used for selecting a control lever, such as SML, by means of code bus 54, additional steps may be provided for selecting additional control devices, by way of other code buses similar to 54.

From the above it will be seen that the impulses applied to the line circuit always begin with a and are followed by a combination of or impulses, dependent upon the code jumper connections and the control lever positions, rendered effective by the particular code determining relay CD which is picked up during a particular cycle. Also, the character or polarity of the impulses in the line circuit is selected by polarity determining relays, PC for a positive impulse and NC for a negative impulse and that these polarity determining relays are positioned during the off periods, in readiness for the application of the preselected polarity during the following on periods.

Operation of stepping reZays.- -It has been explained that the line circuit is normally energized with what may be conveniently termed a polarity, since relay F at the field station is actuated to its right hand position during the normal period. It has also been explained that the polarity applied to the line circuit during the conditioning period is which results in actuating relay F at the field station to its left hand position. It has also been pointed out that the impulses following the conditioning impulse period vary in polarity. Irrespective, however, of

the particular polarity with which the line circuit is energized, relays F and F? in the control oilice are energized by means of circuits above pointed out. Also, irrespective of the polarity of the line circuit impulses which results in actuating relay F at the field station to different positions, relay F'P repeats the actuation of relay F either by means of the circuit extending through contact 22 of relay F direct to the winding of relay P19 or by means of the circuit extending through contact I22 of relay F in the right hand position and front contact I51 of relay SAP At the beginning of the transmitting part of the cycle, marked off by the operation of relays SA and SAP in the control office, relays SA and SAP at the field station shown in Fig. 2, and other similar relays at other field stations are picked up. The half step relay VP in the control office is picked up when the line is deenergized at the beginning of the first off period, this circuithaving been described. The half step relays, VP in the control office and VP" at the field station, are picked up and dropped alternately by successive energizations of the line circuit, that is, they are picked up during the odd "off periods and are dropped during the even off periods. The stepping relays in the control office and at the field station, each take one step for each successive energization of the line circuit, that is, relays IV and IV pick up during the first on period, relays 2V and 2V pick up during the second on period, etc.

Although the stepping relays at the field station operate by means of similar circuits, the description will be directed to those in the control office (Fig. 1). After relay VP is picked up during the first oif period, as above described, the system advances into the first on period by means of a closure of the line circuit, details of which will be later described.

During the first on period, relays F and FF are picked up and a circuit is closed for actuating relay IV extending from front contact 58 of relay SAP, front contact 59 of relay FP, front contact 60' of relay VP, back contact 5| of relay 2V and winding of relay IV, to Relay IV, in operating, closes a stick circuit for itself extending from front contact 58 of relay SAP, front contact 62 of relay IV and winding of relay IV, to It will be understood that this stick circuit for relay IV, as well as the stick circuit for the other stepping relays, is effective to hold the stepping relays in their operated positions, after they are picked up, until the end of the cycle.

Although the above described stick circuit for relay VP is opened at back contact 42 when relay IV is actuated, the VP relay is energized during this period over another circuit extending through front contact 4| of relay PP and front contact 63 of relay VP.

Upon the next deenergization of the line circuit, which advances the system into the second off period, the circuit of relay VP, extending through front contact 4| of relay FP, is interrupted and since its circuit through back contact 42 of relay IV is now open, relay VP is released.

The system is next advanced into the second on period, by means of a closure of the line cir cuit and relay 2V is picked up over a circuit extending from front contact 58 of relay SAP, front contact 59 of relay PP, back contact 69 of relay VP, back contact 64 of relay 3V, front contact 65 of relay IV and winding of relay 2V, to As soon as relay 2V is operated, it closes a stick circuit for itself to stick conductor 66, by way of its front contact 61.

The following deenergized condition of the line circuit, which is the third off period, results in again picking up relay VP by means of a circuit extending from front contact 3| of relay SAP, back contact 4| of relay FP, back contact 68 of relay 3V, front contact 69 of relay 2V and winding of relay VP, to Relay VP closes a stick circuit for itself, through its front contact 43, which is independent of the above described pick-up circuit for this relay through back contact 4| of relay PP.

The system is now advanced into the third on period by a closure of the line circuit. This results in operating relay 3V by means of a circuit extending from front contact 58 of relay SAP, front contact 59 of relay FP, front contact 60 of relay VP, front contact 6| of relay 2V and winding of relay 3V, to Relay 3V operates and closes an obvious stick circuit for itself, by way of its front contact III.

The system advances into its fourth off period when the line is next deenergized. Relay VP is then dropped because its stick circuit, through its front contact 63, is interrupted at front contact 4| of relay FP and its stick circuit, through its front contact 43, is interrupted at back contact 68 of relay BV.

The system is advanced into the fourth on period when the line circuit is next energized. Relay LV is picked up during this period over a circuit extending from front contact 58 of relay SAP, front contact 59 of relay FP, back contact 60 of relay VP, front contact 64 of relay 3V and Winding of relay LV, to Relay LV, in operating, closes an obvious stick circuit for itself by way of its front contact II.

Since the fourth on impulse is the last in the cycle of operations for the present embodiment, the next deenergization of the line circuit continues until the system returns to its normal period. This condition is referred to as the change to normal period, which is an off period because the line circuit is open. During this period, relay LV is up and relay VP is down, therefore, a circuit is effective for holding relay E in its operated position, extending from front contact 3| of relay SAP, front contact 32 of relay LV, back contact 36 of relay VP and winding of relay E, to Relay E, in its operated position, causes the release of relay EP and the actuation of relay FL, by means of circuits above described. Relay PL holds the line circuit open, at its back contact 28 and since there are no additional steps required in this embodiment of the invention, relays E and PL are not immediately dropped to close the line, which results in a long off period.

Since relays F and PP are now down for a cornparatively long interval, relays SA and SAP are released in turn. When relay SAP opens its contact 58, the stick circuits of all stepping relays are interrupted and they are released. Relay SAP also opens the circuit of relay E, at its front contact 3|, which results in the release of the E relay. A circuit is now closed through back contact 31 of relay E for picking up relay EP. The actuation of relay EP opens the circuit of relay PL, which drops and close-s the line circuit at back contact 28. This advances the system into the normal period and it will be obvious that the line is again energized with a. impulse, because relay PC is picked up over the previously described circuit, through back contacts I3, I4,

I5 and I1 of relays VP, 3V, IV and STR. respectively.

In this particular case, where an even number of stepping relays have been shown, the VP relay is already deenergized when the system advances into the change to normal period, but it will be understood that when an odd number of stepping relays are used, the opening of front contact 3| of relay SAP results in the release of relay VP.

It is to be understood that these circuit connections may be extended for as many steps as desired, with the pick-up and stick circuits of the stepping relays and the half step relay extended in an obvious manner. As already mentioned, the stepping relays and the half step relays at the field stations operate in a substantially identical manner and for this reason it is not believed necessary to describe the operation of these relays in detail.

Impulsing of the line for controls-During a cycle of operations for the transmission of controls alone, the off periods are short and the on periods are long. It will now be assumed that the stepping relays IV, 2V, 3V and LV and the half step relay VP operate, as above described and an explanation will be given of the circuits which are effective during this stepping relay operation, to impulse the line circuit.

As above explained, the line is normally energized with a potential, and during the conditioning period it is energized with a potential for picking up relays FP SA and SAP at the stations. During this period, relays FP, SA andSAP in the control office are picked up.

The conditioning period is always a long on because the release of slow relay EP of Fig. 1 must occur after relay E picks up before PL can picked up for opening theline circuit. Opening the line advances the system into the first off period and relay VP is actuated, opening the circuit of relay E at back contact 36 of relay VP, which releases relay E, picks up relay EP and releases relay PL. This closes the line and extends the cycle into its first on period. It will be noted that the 01f period is short because, when the line is opened at the start of this period, it is closed up again as soon as relays F and FP drop, relay VP picks up, relay E drops, relay EP picks up and relay PL drops.

During the first on period relays F, FF and IV are picked up in a manner previously described and relay E is picked up over a circuit extending from front contact 3| of relay SAP, back contacts 32, 33 and 34 of stepping relays LV, 3V and 2V respectively, front contact 35 of relay IV, front contact 36 of relay VP and winding of relay E, to The operation of relay E opens the circuit of relay EP and this latter relay must drop its armature before relay PL is picked up to again open the line. Since relay EP is slow to release, the on period is of long duration.

The operation of relay PL opens the line, which advances the system into the second off period and during this period relay VP is dropped as previously described. This results in the release of relay E, the picking up of relay EP and the dropping of relay PL for again closing the line circuit, which advances the system into the second on period.

From the above it can be seen that relay EP is provided to prolong the energized or on periods. It is also believed that it will be obvious how the line is impulsed by the picking up and release of these various relays on additional steps, in a manner similar to that above explained.

Station selection for controls.For the transmission of controls, the conditioning impulse of each cycle is always while the following impulses are or in accordance with the particular code jumper connections and control lever positions which are effective for that cycle. It will be obvious, by referring to the circuits of Figs. 1 and 2, that these impulses are received at all field stations, since relay PL is not picked up during transmission of controls, which results in the line circuit being extended from station to station, through back contacts similar to back contact I25 of relay PL For convenience in describing the operation of a field station, reference will be made to the circuit of Fig. 2, which illustrates a typical field station in detail and which may be considered as the first station or the one nearest the control office. The application of the first impulse to the line circuit causes the line relay F to actuate its contacts to the left hand dotted position closing a circuit for picking up relay FP extending from contact I22 of relay F and winding of relay FP to Relay FP in turn, closes acircuit for picking up relay SA extending from front contact I23 of relay PP and winding of relay SA to It has been pointed out that this first or conditioning impulse, is long for the purpose of picking up the slow acting relays. The operation of relay SA closes a circuit through its front contact I24 for picking up relay SAP After the conditioning period, the system advances into the first off period, completing a circuit for picking up relay VP extending from front contact I26 of relay SAP back contact I27 of relay FP back contact I28 of relay IV and winding of relay VP to Upon the picking up of the contacts of relay VP its temporary stick circuit is closed from front contact I26 of relay SAP front contact I29 of relay VP back contact I28 of relay IV and winding of relay VP to The system now advances into the first on period with. relays F and FP picked up, the latter relay completing a holding stick circuit for relay VP from front contact I26 of relay SAP front contact I21 of relay FP front contact I 2I of relay VP and winding of relay VP to This holding stick circuit is completed before the temporary stick circuit, including back contact I28 of relay IV is interrupted when relay IV is picked up during this period, because relay IV cannot pick up until relay FP is actuated to close its front contact I20. With relay FP actuated, the circuit for picking up relay I V during the first on period, is completed from front contact I30 of relay SAP front-contact I20 of relay FP front contact I3I of relay VP back contact I 32 of relay 2V and winding of relay IV to As soon as relay IV picks up, it closes a stick circuit for itself including front contact I30 of relay SAP and front contact I33 of relay IV It is not considered necessary to explain the further stepping operations at the field station, since these operations are identical with those explained in connection with the control ofiice.

The first stepping relay IV is picked up during the first on period, which is the period when control No. 1 is executed, but the circuit over'which control No. l is executed does not include a contact of the first stepping relay. The

per winding of delay 381, to

half step relay VP was picked up during the first off period, which is the conditioning period for control No. 1, but the circuit for executing the No. 1 control is not complete until polar relay F is actuated. In other words, the polarity of the first code impulse is preselected in the control office during the first off period and since the relay VP is picked up during this period, this first code impulse. is executed during the following on period by the operation of polar relay F For example, at the field station illustrated in Fig. 2, the first station relay IST is energized over a circuit extending from contact I35 of relay F (actuated to its right hand position because control No. l preselected by code jumper 44 in Fig. 1 was front contact I36 of relay VP back contact I31 of relay 2V No. 1 control bus I34 and upper winding of relay IST to If the first impulse had been (because the No. 1 control bus 45 of Fig. 1 was connected by way of jumper 44 to relay NC instead of relay PC) the actuation of relay F would have been to the left, closing a circuit through its contact I35 in the left hand dottedpos'ition, front contact I39 of relay VP back contact I40 of relay 2V No. 1 control bus MI and lower winding of relay IST to It will be readily understood how the selection of. No. l bus I34 of No. 1 bus MI by relay F results in positioning polar relay IST to its right or left hand position respectively.

During the second on period, relay 2V is picked up and relay F .is actuated to its left hand position by a impulse, closing a circuit from contact I 35 of relay F in its left hand dotted position, back contact I39 of relay VP back contact I42 of relay 3V front contact I43 of relay I V No. 2 control bus I44 and lower winding of relay 2ST to If this impulse in the line should be instead of relay F would close its contact I35 in its right hand position, extending the circuit by way of back contact I36 of relay VP back contact I45 of relay 3V front contact I46. of relay IV No. 2 control bus I41 and upper winding of relay 2ST to The selection of bus I44 or I41 results in the selection of the position in which relay 2ST will be placed during the second on period.

During the third on period, relay F will be positioned to select a circuit through its contact I35 in its right hand position, impulse), front contact I36 of relay VP front contact I3'I of relay 2V No. 3 control bus I48 and up- Or if relay F is positioned to the left, a circuit through its left hand dotted position contact I35 is extended through front contact I39 of relay VP front contact I40 of relay 2V No. 3 control bus I49 and lower winding of relay 3ST to From the above it will be evident that there are a plurality of code determining relays and a set of code jumpers in the control office, one of which relays may be effective to determine the character of the impulses of any particular cycle. During the first part of the cycle, the station selecting relays similar to IST 2ST and 3ST at the field stations are positioned in accordance with the connections of the code jumpers effective for that particular cycle of operations. At each field station a different circuit is selected through the station selecting relays, because each station requires the transmission of a distinctive code and this code is effective to position the station selecting relays in the proper positions, only at the station to be selected for completing circuits through their contacts.

When the fourth control is executed during;

the fourth on period, all the stepping relays will be up and the VP relay will be down. A circuit is now effectiveto position switch machine relay SMR which is a polar magnetic stick relay and which closes circuits in its two operated, positions for selectively operating the switch machine SM to selectively operate the track switch TS If this control impulse is relay F extends the circuit from its contact I35 in its right hand position, back contact I36 of relay VP front contact I45 of relay 3V No. 4 control bus I50, contacts of station selecting relays IST 2ST and 3ST in series, and upper winding of relay SMR to This positions relay SMR to its right hand position for actuating switch machine SM to its normally locked position.

If this impulse in the line circuit is relay F closes a circuit from through its contact I35 in its left hand dotted position, backcontact I39 of relay VP front contact I42 of relay 3V No. 4 control bus I80, contacts of station selecting relays IST 2ST and 3ST in series and lower winding of relay SMR to This latter circuit results in positioning relay SMR to the left for actuating switch machine SM to its reverse locked position.

With the use of only three station selecting relays, as shown in Fig. 2, eight different code combinations are possible, seven of which maybe used for station selection, while the eighth is conveniently referred to as the phantom station code call. It will be understoodthat the code combination for the field station, illustrated in Fig. 2, is as determined by code jumpers 44, 48 and 40 of Fig. 1 being connected to buses Assuming that a impulse actuates a station selecting relay to the right, it will be understood that the code combination predetermined by the code jumper connections of Fig. 1, position the station selecting relays IST 2ST and 3ST in the positions shown in Fig. 2, so that circuits are completed for succeeding impulses which will be effective to position control relays, such as SMR of this'particular station. Also, that control relays, such as SMR at any other station, will not be selected since the station selecting relays at any other station will not have circuits completed to control relays in the positions indicated by the station selecting relays of Fig. 2.

It is obvious that any number of additional steps may be provided for transmitting additional controls to the field station illustrated in Fig. 2, for governing the signals and such other devices as may be required.

End of operating cycle-It has been explained that relays F, FP, SA and SAP and all stepping relays in the control oflice are released during the change to normal period, which follows ticular code determining relay CD, which was picked up during the cycle, is deenergized, so that the next code determining relay in order may be eifective at the beginning of the next cycle, if its corresponding starting button has been actuated and this condition stored by a storing relay (not shown).

Relay PC is picked up at the end of the cycle over a circuit previously described, through back contact I! of relay STR. It is to be noted that field stations can not start a cycle of operations until the system has reached its normal period. This is due to the fact that, even though relay CH drops during a control cycle, it is not eifective to pick up relay PL because the circuit through the lower winding of PL is open at some one of the contacts I46, I45, I36 or I until the system is in its normal or period of blank condition.

TRANSMISSION OF INDICATIONS The selection of field stations for outgoing controls followed by the transmission of these controls is accomplished, as above explained, over the single line circuit extending from the control oflice to the various field stations. The same single circuit is employed, in accordance with this invention, for the transmission of indications to the control office from a station, following the registration of that station having new indications to transmit.

Although this system is of the duplex type, whereby indications may be transmitted from any station to the control office, during the same operating cycle that controls are transmitted to any station from the control office, over the same line circuit, it is convenient to first explain the operation of the system when indications alone are transmitted, during an operating cycle. 7

There may be trains on various portions of the track in the territory supervised by the operator and these trains may enter or leave track circuits at two or more points in the territory at substantially the same time. Similarly, the switches and signals at the various locations may be operated in such a way, by the operator, that several of these traffic controlling devices may assume new positions at substantially the same time. It will thus be evident that when two or more field stations have new indications to transmit at the same time, it is necessary to prevent more than one field station gaining access to the communication circuit, to avoid mutilation of code calls and the transmission of false indications.

The way in which'the field stations are allowed to transmit, one at a time in a predetermined order, is more conveniently explained, following a description of the operation of the system in connection with the transmission of indications from a single field station, assuming that this station is'the only one having new indications to transmit at the beginning of the cycle.

Automatic start by a field station.Referring to Fig, 2, a change in the condition of the detector track section may occur, resulting in track relay T becoming deenergized, assuming this relay to be normally energized as shown in this drawing. likewise, a change in the condition of other traffic controlling devices may occur, but for the purpose of simplifying this disclosure, such other devices are'not shown, but it will be understood that the operation of such other devices results in themementary deenergization of conductor I52 in the same manner that this conductor is momentarily deenergized by the release of relay T The movement of contact I53 of relay T from front to back, or vice versa, momentarily deenergizes the stick circuit of change relay CH allowing this relay to be released. The release of relay CI-I closes a pick-up circuit for relay PL extending from contact I35 of relay F in the right hand position, back contact I36 of relay VP back contact I45 of relay 3V back contact I46 of relay IV front contact I54 of relay CHP back contact I55 of relay CH and lower winding of relay PL to Relay PL closes a stick circuit for itself, which is effective during the time that relay'SAl? is down and which extends from back contact I58 of relay SAP normally closed front contact I59 of relay CHP front contact I60 of relay PL and upper winding of relay PL to The operation of relay PL opensthe line cir-.

cuit at its back contact I25, which results in the release of relay F at the field station and relay F in the control office. It will be noted that relay F opens the above described pick-up circuit of relay PL at its contact I35. This prevents the picking up of any other relay similar to PL at other field stations at this time and since relay VP will be picked up before relay F is again actuated to its right hand position, the pick-up circuits for relays similar to PL are maintained open at back contacts similar to I 36. The pick-up circuits of relays similar to PL are likewise main tained open at back contacts similar to I46 and I45 of relays similar to IV and 3V respectively, all of which results in preventing any other relay similar to- PL being picked up during this operating cycle.

The release of relay F in the control o ifice establishes a circuit for picking up relay STR, extending from back contact ID of relay SA, back contact 22 of relay F, normally closed front contact I2 of relay FF and winding of relay STR, to Relay STR immediately closes a stick circuit for itself extending from back contact 23 of relay LV, back contacts of all CD relays in series, similar toback contact 24, front contact I6 of relay STR and winding of relay STR, to A branch circuit to is established in multiple with contact 23 of relay LV at back contact 56 of relay PL.

During an operating cycle of this class, no CD relay can be picked up, so that the above described stick circuit for relay S-TR is maintained until the last on period, just before the change to normal period. Although the circuit arrangement for preventing the picking up: of any CD relay is not shown in Fig. 1, such a circuit may be similar to that disclosed in the above mentioned prior application Ser. No. 455,304.

With relay STR stuck up and since no CD relay can be picked up, no circuit can be established for operating relay PC. A circuit is effective, however, for operating and holding relay NC throughout this cycle, extending from over the above described stick circuit for relay STR and through the front contact ll of relay STR, to the winding of relay NC. This results in all the impulses in the line circuit being during a cycle of this class.

Referring to the field station circuit, the release of relay F occurring when the line is opened, establishes a circuit for picking up relay PLT extending from contact I35 of relay F in the de-energized position, back contact I62 of relay SA and winding of relay PLT to The operation of relay PLT closes the line circuit at this station, by way of its front contact I63, upper winding of relay L back contact I64 of relay VP back contact I65 of relay IV and resistance coil R to the upper side of the line. This closure of the line circuit results in picking up relay F at the field station, relay F in the control office and lockout relay L0 since this latter releasing), relay L0 lay is energized through its upper winding by current in the line circuit.

This advances the system into the conditioning period, during which control office relays SA, SAP, E, EPT and PL are picked up and relay EP is released, in a manner previously described in connection with the transmission of controls.

Referring to the field station, the picking up of relay PLT opens its back contact I66, which is included in the stick circuit of relay CHP allowing this latter relay to release. Before the release of relay CHP (since it is slightly slow reestablishes a shunt circuit around contact I59 of relay CHP at contact I61 of relay L0 The operation of relay F to the left, since this is a impulse, establishes a circuit for picking up relay FP extending through its left hand contact I22. The actuation of relay FP closes a substitute circuit, at its front contact I68, for holding relay PLT Relays 8A and SAP are picked up during this period, over circuits described in connection with this same period during transmission of controls. The operation of relay SA completes a stick circuit, through its front contact I69 and front contact I10 of relay L0 for holding relay L0 throughout this cycle.

A circuit is established for resetting relay CH before relay SAP is picked up, which extends from back contact I58 of relay SAP front contact I1I of relay L0 front contact I12 of relay SA and upper winding of relay CH to The picking up ofrelay SAP and the opening of its back contact I58, interrupts the stick circuit of relay PL and this latter relay is released, which is effective to close the line circuit through the other stations, by way of back contact I25 of relay PL This conditioning period is likewise long, since the line is closed until slow releasing relay EP in the control office is dropped. The picking up of relay PL in the control office, as above described, opens the line circuit, which is effective to advance the system into the first off period;

The operation of the system is now advanced throughout the different off and on periods, in the same manner previously described in connection with transmission of controls, asfar as the stepping relay and half step relay operations are concerned. In this class of call, however, relay STR is maintained in its operated position, as above mentioned, and relay NC remains picked up throughout the cycle for sending a series of impulses.

It has been mentioned that relays at other stations, similar to PL of Fig. 2, cannot be picked up to interfere with an indication cycle after it has been initiated by a station, of which that shown in Fig. 2 is typical. Since no other relay similar to PL can be picked up, no other relay similar to L0 can be energized, therefore, the code jumper circuits and indication circuits at other stations are not completed during this cycle. During the impulsing of the line circuit, relays similar to F FP SA SAP PLT and the stepping and half step relays locatedat other stations will be actuated in synchronism with corresponding relays shown in Fig. 2.

Registration of a field station-Since a cycle of operations for the transmission of indications results in operating the stepping and half step relays in a manner previously described in connection with transmission of controls, it is not considered necessary to repeat this description.

One of the features of the present invention resides in means for obtaining double the usual capacity of a centralized trafiic controlling system. The following description will be directed to an explanation of the manner in which eight indication code combinations are obtained, in

a system such as illustrate-d in Figs. 1 and 2, in'

which four control code combinations are obtained. It will be understood that for each con-v trol code combination obtained in this system, two indication code combinations are obtainable.

It is believed that this feature of the invention may be best understood by assuming that the field station, shown in Fig. 2, is assigned code (short, long off periods) and (long, short on periods). The above assumption means that the first off period is short (normal) and the second off period is long (abnormal). The first on period is long (normal) while the second on period is short (abnormal). This is brought about at the field station by omitting the jumper connection of No. 1 off bus I13, which results in the first off period being normally short. N0. 1 on bus conductor I14, likewise has the jumper omitted which results in a normally long first on period. No. 2 off bus I15 has a jump er I90 connection completed to which results in the second off period being abnormally long. No. 2 on bus I16 has a jumper I93 con-- nection completed to which results in the second on period being abnormally short. The No. 3 on bus I11 leads to the back contact I18 of relay T so that the third on period will record, in the control oflice, the position of'relay T after this station has been registered in. the control office.

Other indication buses, leading to bracket 113,

may be connected or disconnected from potential in a similar manner for obtaining additional indications. It is believed however, that an example suificient for the understanding of this operation is given in connection with the above enumerated off and on periods.

From the above it will be seen that a de-energized' ofi' bus results in a short off period, while an energized off bus results in a long off period. A de-energized on bus results in a long on period, while an energized on bus results in a short on period.

Assuming that synchronous stepping occurs in the control office (Fig. 1) and at the field station (Fig, 2), reference will be made to the above table and an explanation will be given how the combination of short and long off and .on periods are obtained, together with the conditioning of the pilot relays in the control office, for selectively registering the desired station.

The first off period which follows the con--v ditioning period is assumed to be short. This is because the jumper connection (Fig. 2) between bus I13 and (+)'is omitted. Relay CI-IlE' -is, down during a cycle of this class so that the'only circuit for picking up the line pulsing relay PL is by way of its upper winding. During the ,oflf

of relay FP front contact I 85 of relay PLT and taining circuit is completed to energize relay PLT extending from front contact I58 of relay SAP back contact I19 of relay PL and winding of relayPLT to A circuit may be traced from the No. 1 off bus I'I3, back contact I8I of relay 2V front contact I82 of relay VP front contact I83 of relay L0 back contact I84 of relay FP front contact I85 of relay PLT and upper winding of relay PL to Since the jumper connection of bus I13 is omitted, the above traced circuit is not effective to energize relay PL so that the line circuit is not opened at the station under this condition.

Inasmuch as the line circuit is not opened at the station, it is energized at the control oflice by the release of relay PL, which follows the release of relay E and the picking up of relay EP. Relay PL closes the line at its back contact 28. This results in a short or normal first off period.

The system advances from the first off period to the first on period in a comparatively short interval of time, and the No. 1o1f indication, Which was conditioned (short) during the first off period, will be executed in the first on period. Relay EPT in the control ofiice is not released when the off indication is short, because the system advances into the on period and picks up relay F, before relay EPT has time to drop its armature, thus establishing a holding stick circuit for relay EPT through its front contact 39.

In the first on period, the No. 1 short off indication, above described, is executed by extending a circuit from (B), front contact I2 of relay EPT, front contact I3 of relay F, back contact 14 of relay E, front contact I5 of relay VP, back contact T6 of relay 2V, No. 1 off indication bus .17 and winding of relay IPF, to (CN) Current through polar magnetic stick relay IPF is in such adirection that it will be positioned to the left, as shown in Fig. 1.

During the first on period, the No. 1 on indication is conditioned by a circuit extending from bus I14, through front contact I86 of relay IV back contact I 87 of relay 3V front contact I88 of relay VP front contact I89 of relay L0 frontcontact I84 of relay FP front contact I85 of relay PLT and upper winding of relay PL to But since bus I14 is not connected to relay PL is not picked up. The line is therefore,

not opened at the field station during this period, so that it remains closed for a long interval, marked off by therelease of relay EP in the control office, which picks up relay PL and opens the line at its back contact 28.

' The system next advances into the second off period, where on indication No. 1, above described, is executed. The on indication No. 1

is long and since relay EP is down, a circuit is closed for executing this long indication, extending from (B back contact I8 of relay EP, back contact 79 of relay F, front contact 51 of relay E,

back contact 88 of relay LV, back contact BI of relay 3V, back contact 82 of relay 2V, front contact 8301 relay IV, No. 1 on indication bus 84 and winding of relay IPB, to (CN). Current in this circuit is in a direction to position relay I PB to the left as shoWn.

During this, the second off period, off indication No. 2 is conditioned, by means of a circuit extending from jumper I90, No. 2 o bus I15, front contact I9I of relay IV back contact I92 of relay 3V back contact I82 of relay VP front contact I83 of relay L0 back contact I84 upper winding of relay PL to Due to this completed circuit, relay PL will be picked up which results in opening the line at the field station, at back contact I25. Since relay IV is up, the line circuit is open at its back contact I65. The control ofiice attempts to energize the line, in the manner above described for the first off period, by dropping relay PL in a comparatively short time. The field station, however, maintains the line open at contact I25 of relay PL and this relay opens the circuit of relay PLT at back contact I19. Relay PLT releases, after a comparatively long interval, and opens the above traced circuit through the upper winding of relay PL at contact I85. Relay PL drops and energizes the line circuit.

This extends the second foif period, making it abnormally long. When the line is finally enerized by relay PL at the field station dropping and closing its back contact I25, the system is advanced into the second, on period, where the No. 2 off indication is executed. After relay E was dropped, during the second off period, relay F was not again picked up in time to complete the sustaining stick circuit for relay EPT through its front contact 39. This allows relay EPT to release, completing the circuit for executing the No. 2 off indication (long), extending from (B+), back contact 72 of relay EPT, front contact 13 of relay F, back contact 14 of relay E,

back contact 15 of relay VP, back contact 85 of relay 3V, front contact 86 of relay IV, No. 2 off indication bus 81 and winding of relay ZPF, to (CN). Current in this circuit is in such a direction that relay 2PF will be positioned to the right as shown in Fig. 1.

During the second on period, the No. 2 on indication is conditioned. Code jumper I93 is connected to and a circuit is completed from this code jumper, by way of No. 2 on indication bus I16, front contact I94 of relay 2V back contact I95 of relay 3V back contact I88 of relay VP front contact I89 of relay L0 front contact I84 of relay FP front contact I85 of relay PLT and upper winding of relay PL to Relay PL is .picked up and held until the release of relay PLT which occurs in a comparatively long interval of time, after its circuit is opened at back contact I79 of relay PL The picking up of relay PL opens the line circuit at the field station, before it would otherwise be opened in the control ofi'ice, by the dropping of slow relay EP. This results in reducing an otherwise normally long on period to an abnormally short on period.

Opening the line circuit advances the system into the third off period, where the short No. 2 on indication is executed. Relay EP did not have time to drop during the second on period and the system advances into the third off period with relay EP up. The release of relay F closes a circuit for executing the No. 2 on indication, extending from (3+), front contact I8 of relay EP, back contact I9 of relay F, front contact 51 of relay E, back contact 88 of relay LV, back contact 8I of relay 3V, front contact 82 of relay 2V, No. 2 on indication bus 88, and winding of relay 2PB, to (CN). The current in this circuit is in such a direction that relay ZPB will be positioned to the right, as shown in Fig. 1. Relay E drops during this, the third off, period and closes a circuit for energizing relay EP, before this latter relay has time to release.

Examples have been given of the conditioning and executing circuits for short and long off and on periods. It is believed that these examples are sufiicient to show how these off and on periods may be varied in order to obtain other code combinations. It is obvious that No. 1 off indication bus I13, if connected to by a jumper, would result in a long first off period. Under this assumption, relay IPF in Fig. 1 would be positioned to the right, because relay E'PT would be dropped to apply (3+) to the No. l 011' indication bus 11.

It should be understood that additional pilot relays, similar to IPF, IPB, etc., may be provided and positioned on any desired number of steps, but forthe sake of simplicity, only two have been shown'operated during the ofi periods and two operated during the on periods.

It will be obvious that with two steps, sixteen different code combinations or selections through the station registering pilot relays may be made. It will be understood, however, that the sixteenth or last combination, composed of all normal periods, that is, short off periods and long on periods throughout a cycle of operations, cannot be used for station registration for indications, since this is the inherent combination obtained during the transmission of controls alone, which must result in the failure of the system to register any station for inbound calls.

Transmission of indications-After having registered the particular station in the control office, which has indications ready to transmit, the remaining steps of the cycle are employed for the transmission of such indications.

For example, the No. 3 on indication bus I1! is shown connected to a normally open back contact H8 of relay T During the third on period, bus IT! is extended by way of front contact l 8'| of relay 3V front contact I88 of relay VP front contact I89 of relay L0 front contact I84 of relay FP front contact I85 of relay PL'I and upper winding of relay PL to If the track relay T is in the position shown in Fig. 2, this circuit is inefiective to energize relay PL with the result that this third on period will be normally long, for the reason described above in connection with the first on period.

Therefore, relay EP in Fig. 1 will be down during the fourth off period when the No. 3 on indication is executed. This completes a circuit from (13-), through back contact 18 of relay EP, back contact 18 of relay F, front contact 51 of relay E, back contact of relay LV, front contact 8| of relay 3V, No. 3 on indication bus 89, contacts 90, 9|, 92 and 93 of the pilot relays, positioned as above described, and winding of indication relay IRF, to (CN). Current over this circuit results in positioning relay IRF to the left for displaying indication lamp 1.

If track relay T is down when this indication is conditioned, the circuit completed through its back contact I18, during the third on period, is eifective to pick up relay PL over a circuit which has previously been traced. Relay PL opens the line at the field station, before waiting for relay EP in the control office to drop and pick up relay PL for opening the line, so that a short No. 3 on indication is conditioned during the third on period.

During the fourth 01f period, since relay EP did not drop, a circuit is extended from (B+), front contact 18 of relay EP and the remainder of the circuit previously described, through contacts of the pilot relays, resulting in positioning relay IRF to the right.

It will now be obvious how additional indication, buses, IB of Fig. 2, may be variably connected for variably selecting additional pilot or indication relays, similar to IPB, IPF, IRF, etc., in the control office.

End of indication cycle.The step-by-step operations and the impulsing of the line circuit during an indication cycle are similar to' those operations during a control cycle and the line is opened, following the last impulse or on period, in a manner similar to that previously explained, which allows the relays to assume normal positions. control oflice opens the pick-up circuit of relay SAP and at the same time establishes a stick circuit for relay FP, for holding this latter relay The release of relay SA in the" in its operated position until after the start of the next cycle.

The release of relay SA at the field station opens the circuits of relays L0 and SAP and they are dropped. The release of relay SAP at the field station opens the stick circuit of the stepping relays and the half step relay. and they are restored to normal.

It has been explained that relay CH is picked up during the conditioning period. As soon as they system is advanced into its normal period, a

circuit for picking up relay CHP is efiective,

extending from contact I35 of relay F in the right hand position,back contact l36 of relay VP back contact I45 of relay 3V back contact I46 of relay IV and lower winding of relay CHP to Relay CHP is again stuck up through back contact I66 of relay PLT until after the start of the next cycle. l

Lock-out between field stations.-As previously mentioned, it may happen that changes take place at several field stations simultaneously or in rapid succession, so that more than one field station will have new indications to transmit at the beginning of a cycle. Inv order to prevent more than one field station obtaining access to the line during any cycle of operations, lock-out means are provided at each field station effective to give control of the line to the field station nearest the control oflice, under the above conditions.

It has already been explained that the instant CH may be down at the same time,- while the system is in its normal or period of blank condition. In this case, two or more relays similar to PL can be picked up, over circuits similar to those previously described for picking up relay PD of Fig. 2.

' It is believed that the look-out feature may be best understood by assuming that two relays similar to PL are picked up at the same time and explaining how only the station nearest the control ofiice is effective to transmit indications over the line circuit under this condition. It will be understood that the operation is the same when more than two relays, similar to PL are picked up, since only the station nearest the control 10 tions are dropped, the two relays similar to PLT are picked up, over circuits similar to those previously described in connection with Fig. 2. The picking up of the relay similar to PLT at the station nearest the control oilice, closes the circult of the line through the upper winding of the relays to drop away.

lock-out relay similar to L0: at' this station. At the same time, the relays similar to PLT at both stations, open the stick circuits of relays similar to CHP at both stations allowing these two They are slightly slow to release so that the look-out relay similar to L0 at the station nearest the control oflice, has time to be picked up and establish a sustaining stick circuit for the relay similar to 2 5 PL at a front contact similar to I61, before this stick circuit is broken by the opening of a back contact similar to I59 of the relay similar to CHP The lock-out relay similar to-LO at the farther station, does not get current, therefore, when the relay similar to CHP at the farther station drops its armature, there is no circuit for holding the relay similar to PL at the farther station and it is released, which is effective to complete the closure of the line circuit through the other stations.

Current over the line circuit is flows through the station nearest the control office and causes relays similar to F FP SA and 'SAP at this station to be picked up. Since the relay similar to PLT was picked up at the time the line was opened, the circuit at this nearest station is closed through front contact I63 of this relay and the upper winding of the look-out relay similar to L0 The relay similarto SA establishes a stick circuit to hold the look-out relay at its front contact, similar to I59 and this circuit is maintained throughout the operating cycle.

-When the relay similar to SAP, at the station nearest the control office picks up, the relay similar to PL is dropped, because its stick circuit is interrupted at a back contact similar to I58. It will be recalled that after the relaysimilar to FI leaves its right hand contact, no relay similar to PL can be .picked up through its lower winding.

It will now be evident that the station nearest the control office is the only one with its relay similar to L0 picked up, so that this is the only station where the indication buses are connected through front contacts similar to I83 and I89 of the look-out relay. This is the only station effec tive to transmit indications to the control oflice by impulsing the line circuit.

The relay similar to CH at the station nearest the office, is again picked up when the relay similar to SA is picked up, over a circuit which has been previously described, including a front contact of the lock-out relay. It will thus be seen that other relays similar to relay CH will remain down at those other stations having new indications to transmit, until they each get a chance to obtain access to the line. Since the relay similar to CH at the station nearest the control ofiice is picked up at the beginning of the cycle, it may thereafter be again released fora subsequent seizure of the line circuit, if additional new indications are to be transmitted from this station, at the start of the next operating cycle.

From the above it will be understood that, irrespective of whether the new indicationsto be transmitted occur simultaneously or sequentially, the field station nearest the control office will be the only one which obtains current for energizing its lock-out relay and for impulsing the line. Those stations farther away from the control ofiice will not have their lock-out relays picked up,'their relays similar to PL will not be picked up, which results in the line circuit being conductively completed through back contacts similar to I25, of relays similar to PL at those other stations.

An important feature of the present invention relates to the organization of the circuits in a two wire lock-out system to maintain synchronous stepping at all stations during a cycle, at

the start of which there are a plurality of stored field and office start conditions. This is necessary in a duplex system in order that controls may be properly transmitted during the same cycle that the lock-out feature has been effected.

From the above description relating to the lock-out feature, it will be noted that the line circuit is maintained closed up to the station which obtains access to the line and is opened to stations beyond this point. It therefore, be-

comes necessary to so arrange the circuits that the two difi'erent conditions of the line (open and closed) at the different stations do not resuit in causing the stepping and other'operations at these different stations to get out of synchronism.

Under the above conditions, current of polarity flows to the field station nearest the office during the conditioning period and picks up relays F FP SA and SAP as above described.

Corresponding relays are picked up' at other stations toward the control office but at stations farther out along the line these corresponding relays do not pick up (due to the line circuit being opened at back contact I25 of relay PL until relay PL drops.

When relay PL is released (by the picking up of relay SAP the continuity of the line is transferred from the path through the winding of relay L0 to the path through the line circuit extending through the other stations farther out the line. Relays corresponding to relays F FP 3A and SAP at those other stations are now picked up by this conditioning impulse and the cycle is carried through with all stations working in synchronism. Since relay VP picks up during the first off period and since relay IV is picked up before relay VP drops, the impulsing of relay PL is effective to open the line which extends through all stations at back contact I25. This is done without closing the line through the winding of the look-out relay because this branch of the circuit will be main tained open at contact I64 of relay VP or contact I65 of relay IV Two-way transmission-It has been pointed out that control and indication cycles may each .occur separately or simultaneously. The operation for each of these cycles alone has been described in detail and it will now be explained during the time the system is at normal and during the time up to the pick-up of relay SA, during the conditioning period. After the pickup of relay SA, the circuit for picking up the start relay S'IR. is interrupted at back contact In of relay SA, if a field station has initiated the cycle.

The actuation of a starting button in the control ofiice and the picking up of its corresponding CD relay results in picking up relay STR and sticking it until the first off period, when it is dropped, as has been described in connection with the transmission of controls alone. For the transmission of indications alone, relay STR' is picked up and stuck up until the end of the cycle, over a series stick circuit, extending through back contacts of all CD relays. This has been described in connection with the transmission of indications alone.

For a duplex cycle, when controls and indications are both transmitted during the same cycle, relay STR will be picked up by means of the previously described circuit, through front contact I l of a CD relay, or back contact 22 of relay F. Relay STR will be dropped during the first off period in this case, because some CD relay will be up to open the series stick circuit above described.

At the start of a duplex cycle, station relays PL PLT and LO are picked up, relay CHP is dropped and relay L0 is stuck up until the end of the cycle, all of which has been described in connection with the transmission of indications alone. The lockout feature is likewise effected in the same manner as described for the transmission of indications alone.

During a duplex cycle, the impulse applied to the line circuit, during the conditioning period, is and the following impulses are or determined by the particular CD relay in the control cfilce which is up. The ofi periods are short (normal) or long (abnormal) and the on periods are long (normal) or short (abnormal), as determined by code buses selected by a lockout relay, similar to L0 which is up at a particular field station. I

It is therefore, evident that since only oneCD relay in the office and one lockout relay at a field station can be up at one time, during a cycle of operations and since transmission of controls and transmission of indications take place during separate and distinct conditions of the line, these transmissions are independent of each other and can be incorporated into the same operating cycle for obtaining the duplex feature.

The resulting cycle of operations, insofar as the transmission of impulses over the line circuit, the application of the short and long off and on periods and the conditioning and executing circuits are concerned, are the same as described for separate control andindication cycles.

In a. system of this character where stepping impulses are applied to the line circuit for the transmission of indications alone, it will be evident that some means must be provided to prevent such impulses from, being effective to control or govern the selection or transmission of controls to any field station.

Similarly, when the system is transmitting controls alone, some means must be provided to prevent the normal off and on periods from being efiective to register indications in the control ofiice from any field station, so that a This may be termed a code call for'a phantom station.

Similarly, when indications are being transmitted alone during an operating cycle, all of the impulses in the line circuit are and that code call corresponding to all impulses is not employed'for the selection of any field station. This combination or impulses may be termed a code call for a phantom station.

SUMMARY -The present embodimenthas been described,

more particularly with reference to the character of the devices employed in a centralized traffic controlling system and their respective functions, 1 together'with .typical operating conditions and it will be understood that all possible combinations Sic of circumstances can not be considered in detail.

The system may be initiated into a cycle of operations from a normal condition, by. a change in condition either at the control ofiice or at any one or more of the field stations. Such change in condition causes, the system-to go through an operating cycle, comprising an initiating and lockout period, a conditioning period, a transmitting portion of the cycle, referred to as the ofi and on periods and the change to norma period at the end of the cycle.

During the initiating and lockout period, the

various relays are positioned and the system is started through a cycle. Changes may occur at any time during this period but at the time the line relays, similar to F at the field stations, are released and from this point on during the cycle,

changes at any field station are ineffective to govern the character of the cycle. Likewise, after the picking up of any CD relay in the control office, the following cycle of operations determines the character of such cycle to be for the transmission of controls. Indications may be transmitted along withcontrols during this cycle if a lookout relay is upat the start of the cycle.

Acycle of operations, therefore, may be for the transmission of controls and/or the trans mission of indications. mitted by and impulses applied to the line circuit, while the indications are transmitted by varying the time intervals during which the line circuit is energized and de-energized.

The lockout period is marked off by the dropping of relays similar to F at the field stations and in the event that two or more stations are ready to transmit newindications at the start of an operating cycle-only one station is eifective to obtain control of the line circuit, since only one lockout relay can. be up'at any one time.

The present system also discloses means whereby each field station lockout relay is restored to normal at the end of a cycle, so that all field stations will be synchronized at the beginning of each cycle.

Following the initiating and lockout period, the conditioning period is effective to condition the cycle demarcating relays SA,'SA SAP and SAP in the control office and at the field sta- The controls are transtions, as well as conditioning the line impulsing relay for starting the series of impulses.

The transmitting part of the cycle follows, during which each successive impulse applied to the line circuit results in the energization of a three-position polar magnetic stick type relayat each field station for effecting the selection of a particular station and for receiving controls. The stepping relays at the control office and at the several stations take their steps during the on periods, when the line is energized. The half step relays at the control office and at the several field stations are shifted during the off periods, when the line is de-energized. During the odd ofi periods, these half steprelays are picked up and during the even "off periods, they are dropped.

For the transmission of indications, the line circuit is either energized for a normally long period or an abnormally short period and is deenergized for a normally short period or an abnormally long period, to position message receiving relays in the control ofiice. These message receiving relays are indicated in Fig. 1 as EPT, for receiving the messages during the off periods and EP, for receiving the messages during the on periods. The relay (EPT) which receives the messages during the off periods, executes these messages during the next succeeding on periods. The relay (EP) which receives the messages during the on periods, executes these messages during the next succeeding ofi periods.

In other words, indications are conditioned twicefor each step, once during the off periods and once during the on periods. These two conditions are made effective, when they are executed, to position two-position polar magnetic stick type relays, indicated IPF, 2P1, IPB and 2PB in Fig. 1. Thus, the stations and indications are registered in the control ofiice over a single line circuit, which is also used for transmission of controls and these indications are transmitted twice as fast as the controls. Such a system not only renders the most efficient use of the transmission line, but it is particularly adaptable tocentralized traflic controlling operations, since a larger number of indications than controls are usually required for the proper supervision in such asystem.

At the end of the transmitting part of the cycle, the line circuit is maintained open in thecontrol ofilce for a prolonged period of time, until the slow acting relays SA and SAP are de-energized, which provides sufficient time for restoring the relays to normal at the control ofiice and at all of the field stations.

Various other novel features of the present invention reside in the circuit arrangements disclosed, such as the transmission of controls during the on periods by conditioning the polarity selecting relays in the control office, by

way of contacts on stepping relays which do not shift when the control is transmitted. In other words, the polarity of a control impulse isselected during an off period and is maintained during the subsequent on period, notwithstanding the fact that a. stepping relay is picked up during the subsequent on period.

Although one specific embodiment of the invention has been shown, it is to be understood that various rearrangements of the circuits may be made without departing from the spirit of the invention. For example, the familiar SO relayrarrangement, disclosed in the above mentioned prior application, Ser. No. 455,304, for dropping out all field stations except the one desired during transmission of controls, could be'used insteadof the station relays IST 2ST and 3ST of Fig. 2.

Having thus described one specific embodiment of a centralized traific controlling system, it is desired'to be understood that this particular form has been selected to facilitate in the disclosure of the invention, rather than to limit it and it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form disclosed, without in any manner departing from the spirit or scope of the present invention, except as limited by the appended claims.

What we claim is:

1. In a centralized traflic controlling system, a control ofiice, a field station, a line circuit connecting said control office with said field station, step-by-step mechanisms at said control office and at said field station, means for operating said mechanisms in synchronism by energizing said line circuit with a series of impulses, means at said control office for controlling said line circuit to provide a normally long impulse, means at said field station for controlling said line circuit to provide an abnormally short impulse, and means responsive to a combination of said long and short impulses during the operation of said mechanisms for registering said field station in said control ofilce.

2. In a centralized traffic controlling system, a control oflice, a field station, a line circuit connecting said control oflice with said field station, step by step mechanisms at said control office and at said field station, means for operating said mechanisms in synchronism by a series of impulses applied to said line circuit, means at said control ofiice for controlling said line circuit to provide a normally long impulse and a normally short time interval between impulses, means at said field station for reducing the length of said long impulse and for extending the length of said short time interval to form a code combination, and means controlled by said code combination for registering said field station in said control oflice during the operation of said mechanisms.

3. In a centralized trafiic controlling system, a control ofiice, a field station, a normally energized line circuit extending from said control oifice to said field station, means at said control oiTice for de-energizing' and energizing said line circuit to form a series of equally time-spaced impulses of equal duration, step by step mechanisms at said control office and at said field station operated in synchronism by said impulses, code selecting means at said field station operable successively by said mechanism to change said impulses to a series of unequal time spaced impulses of unequal duration, and means at said control office for registering said unequal time spacings and impulses during the operation of said mechanisms.

In a centralized traffic controlling system, a control ofiice, a plurality of field stations, a line circuit connecting said control ofiice with said field stations, step-by-step mechanism at said control ofiice and at said field stations, means for energizing said line circuit with a series of impulses of distinctive character, means responsive to said impulses for operating said step-bystep mechanisms in synchronism, means for varying the lengths of said impulses during the operation of said mechanisms, means responsive to the character of said impulses for selecting one of said field stations during the operation of said mechanisms, and means responsive to the lengths of said impulses for registering another of said field stations in said control office during the operation of said mechanisms.

5. In a centralized traific controlling system, a control ofiice, a plurality of field stations, a line circuit connecting said control oflice with said field stations, step-by-step mechanism at said control ofiice and at said field stations, means for energizing said line circuit with a series of time spaced impulses of distinctive character, means responsive to said impulses for operating said step-by-step mechanisms in synchronism, means for varying the lengths of said impulses and the time spaces between the impulses during the operation of said mechanisms, means responsive to the character of said impulses for selecting one of said stations during the operation of said mechanisms, and means responsive to the variations in time between and the lengths of said impulses for registering another of said stations in said control office during the operation of said mechanisms.

6. A selector system for transmitting messages from a central ofiice to a plurality of field stations, in which a line circuit is energized by a series of characteristic impulses applied thereto, odd and even stepping relays, circuit means controlled by said impulses for alternately actuating odd and even stepping relays in succession, each odd relay being actuated during an odd impulse and each even relay being actuated during an even impulse, a circuit including contacts of said odd stepping relays and exclusive of contacts of said even stepping relays, and means including said circuit for selecting the character of said even impulses.

7. In a centralized traific controlling system, a control ofiice, a plurality of field stations, at line circuit connecting said control office with said field stations, step-by-step mechanism at said control office and at said field stations, signalling devices at said field stations and indicating devices at said control ofiice, means at said control ofiice for applying a plurality of time spaced impulses of distinctive character to said line' cirsuit for effecting an operating cycle of said mechanisms, means at each of said field stations for varying the time spaces between said impulses and for varying the lengths of said impulses, means at each of said field stations responsive to the character of said impulses for selecting the associated field station and for operating the signalling devices thereat during an operating cycle of said mechanisms, and means at said control office responsive to the variations in time between and the lengths of said impulses for registering a selected field station in said control ofiice and for operating its associated indicating devices during said operating cycle.

8. In a centralized traific controlling system, a control office, a field station, a line circuit connecting said control ofiice with said field station, step-by-step mechanisms at said control ofiice and at said field station, means for operating said mechanisms in synchronism by energizing said line circuit with a series of impulses, means at said control oflice for controlling said line circuit to provide normally long impulses, means at said field station for transmitting code messages to said control ofiice by controlling said line circuit to change said normally long impulses to abnormally short impulses, an impulse registering relay, means responsive to. the length of said impulses for distinctively operating said impulse registering relay during the operation of said mechanisms, and means responsive to the distinct operation of said impulse registering relay for registering said code messages in said control office.

9. In a remote control system, an oifice and a station, a line wire connecting the office and station, stepping apparatus for transmitting a series of time-spaced impulses of current one at a time in sequence from the office to the station over said line wire, a series of movable devices at the station, a series of indicators at the ofiice including one for each device, means at the station for selectively controlling the length of each impulse and of each interval between impulses of said series, means at the ofiice for selectively controlling the relative polarity of each of said impulses, means for controlling said devices each in accordance with the relative polarity of a selected impulse of said series, means for controlling certain of said indicators of said series each in accordance with the relative length of a selected impulse of said series, and means for controlling the remaining indicators of said series each in accordance with the relative length of a selected interval between impulses of said series.

10. In a remote control system, two stations connected by a single line circuit, a series of movable devices at each station, means for transmitting over said line circuit a series of timespaced impulses of current, comprising means at one station for selectively controlling the length of the impulses and of the intervals between impulses, and means at the other station for selectively controlling the relative polarity of the impulses, means for controlling a selected device at one station to one position or another in accordance with the relative length of a particular impulse of the series, means for controlling another selected device at said station to one position or another in accordance with the relative length of the interval between said impulse and the next impulse of the series, and means for controlling a selected device at the other station to one position or another in accordance with the relative polarity of said impulse.

11. In a remote control system, two stations connected by a single line circuit, a series of movable devices at each station, means for transmitting over said line circuit a series of timespaced impulses of current, comprising means at one station efiective to selectively control the length of each impulse of said series, and means at the other station effective to selectively control the relative polarity of each impulse of said series; means effective to control the devices at said one station each in accordance with the relative polarity of a particular impulse of said series, and means effective to control the devices at said other station each in accordance with the relative length of a particular impulse of said series.

12. In a remote control system, a receiver comprising a line relay adapted to be energized repeatedly by consecutive elements of a series of timed impulses of current, a slow release relay adapted to become released if the line relay remains energized 'for more than a predetermined time interval, a series of polarized indication relays, one for each element, and means rendered eiTective each time the line relay becomes deenergized for energizing a selected one of said indication relays to one position provided said 

